Electrode in discharge tubes



A ril 25, 1933. ZECHER A 1,906,037

ELECTRODE IN DISCHARGE TUBES Filed Jan. 6, 1926 Patented Apr. 25, 1933 kept very small.

SIGNORS, BY HESNE RATION OF NEW YORK ASSIGNMENTS, T0 GENERAL ELECTRIC COMPANY, A CORPO- ELECTRODE IN DISCHARGE TUBES Applicationflled. January 6, 1926, Serial 1T0. 78,590, and in the Netherlands It is known to use magnesium in gasfilled discharge tubes as well as in vacuum tubes for the absorption of ingredients injurious to the discharge whilst the use of magnesium as a material for constituting the electrodes, materially decreases the starting voltage of the tube. It has therefore been proposed already to constitute one or more of the electrodes in discharge tubes, at least partly, of magnesium. Such electrodes, however, have several disadvantages. Thus, for example, the life of these electrodes is very short because they soon disintegrate if the current density at the surface of the electrodes is not Besides, in gasfilled discharge tubes the disintegrating magnesium absorbs not only the lIljIlIlOllS ingredients but also the gaseous filling itself, so that the pressure of the gas gradually decreases.

Now the invention has for its ob'ect the manufacture of magnesium electrodes which do not have the said disadvantages and it can more particularly be applied to gasfilled j tubes in which the glowing effect is produced by the positive column.

ccording to the invention the discliar e e comprises one or more bodies whlch su tub stantially consist of magnesium and which during or after the exhaustion of the tube are heated to'such an extent that the magnesium voltalizes or disintegrates and de- Egsits on the wall of thetube in the neighurhood of one or more conductors serving to lead the current through the wall of the tube and in conductive connection with the said conductors.

The body may be heated in diflerent ways. Thus, for example,

two leading-in conductors and which-volatilizes when galvanically heated. In this case,

the disadvantage that after however, there is v i magnesium has been volatilized,

part of'the the helix breaks whilst the deposit on the wall is still insuflicient. Also themagnesilim may be disintegrated by init1at1ng a discharge between two magnesium bodies contages. During the discharge,

- plled a magnesium helix may,

i be provided which, at its ends is connected to such icured to a leading-m conductor; During the March as, 1925.

bodies disintegrate or volatilize and a layer 0 magnesium is deposited on the wall of the tube. The disadvantage of this method is that during the forming, the layer contributes already to the discharge so that in the thinner places the layer on the wall of the tube is galvanically heated and volatilizes. It is therefore advisable to heat the magnesium bodies by a high netic field, which heating-permits tovolatilize a suflicient quantity of to concentrate the deposition on the wall to a good conducting layer 'in the immediate vicinity of one or more leading-in conductors.

Applicant has noticed that on applying a frequency magc0 magnesium and I said layer is comparatively thin), the contact of this layer with the leading-in conductor often leaves much to bedesired.

It is therefore advisable to coat the leadingin conductor and the wall portions lying in its neighbourhood, prior to the exhaustion of the tube with a conductive layer owing to which a safe contact with a'magnesium deposited on the wall is ensured. For constituting the conductive layer graphite should preferably be used which may be apas an emulsion in water or in some binding agent for example aniline. During the exhaustion of the tube part of the ingredients injurious to the discharge and ina troduce'd into the tube together with the binders, are pumped away, which is favourably influenced by heating the wall of the tube and thereto.

they cannot exercise any detrimental in-' fluence.

'The magnesium body should preferably be fixed on a rod of any material susceptible of being readily deprived of occluded gases,

for example as iron, said rod being sevolatilization' of'the ma esium this red is then already sufliciently fe prived of occluded gases. Besides, with regard to' the current intensity required, the layer deposited on the a wall may be chosen such that during the opinvention is already eration of the tube the rod does not contribute to the discharge and consequently neither is heated to a high temperature.

The discharge tube comprising one or more electrodes constituted in accordance with the process of the invention, offers the advantage that it has a long life since owing to the large surface of the electrode the temperature of the latter is not raised very much so that the material deposited on the wall disintegrates or volatilizes only in a slight meas- Besides, any ingredients injurious to the discharge and present in the tube, are absorbed while the layer acting as an electrode is being applied and during the operation of the tube and the operatin voltage and the starting voltage of the tu e are materially smaller than is the case with the usual electrodes. In a mode of realization of the invention the wall of the tube in the neighbourhood of the leading-in conductors is given such a shape that the magnesium which has deposited on the wall and which disintegrates or volatilizes during the operation of the tube, substantially deposits again on the wall portion coated already with magnesium. Owing to this the volatilization of magnesium which with the electrodes according to the small, does not exercise any detrimental influence on the life of the tube as the layer once produced remains intact. For thi's'purpose the wall of the tube in the neighbourhood of the leading-in conductors should preferably be made substantially spherical. Besides, in order to prevent any deposition of magnesium on the wall portions which do not act as an electrode, the tube near the portion acting as an electrode, may be kinked.

The invention will be more clearly understood by referring to the accompanying drawing in which Figure 1 represents a discharge tube in which the glowing effect is produced by the positive column, said tube comprising electrodes constituted in accordance with the process of the invention and Figure 2 shows a detail of one of the electrodes in such'a' tube.

In the drawing the numeral 1 refers to a glass tube which at both sides is kinked and which is provided with spherical ends 2. In

4 fixed to the rod each end 2 is sealed a leading-in wire 3, for example, of platinum or of any other material allowing of being readily sealed in glass,

and havin a coefficient of expansion slightly different om that of glass. To the leadingin wire is fixed, for example by welding, a

f U-shaped rod 4 of iron on which a magnesium helix 5 is provided. A mica screen 6 may be 4 inorder to limit the deposition of magnesium as much as possible to the wall of the sphere 2. A

Before the end 2 is sealed in the tube 1, a portion of the leading-in wire 3 as well as the glass wall in the nearest proximity of this wire is coated with a layer 7 of conductive material. Preferably an emulsion of graphite in water should be used for this purpose. The ends 2 are then sealed to the tube 1, whereupon the tube is exhausted in the known manner and is provided with a gaseous filling for which purpose frequently neon under a pressure of some millimetres of mercury is used.

During or after the exhaustion operation a coil (not shewn in the drawing) is arranged around each end 2, in which coil a high frequency magnetic field of such intensity is excited that the magnesium helix 5 volatilizes and on the wall of the tube a magnesium layer 8 is formed which also covers the conductive layer 7 After the magnesium helix 5 has substantially been volatilized and the tube has been closed by fusion, the discharge tube is ready for use and may be connected to some source of potential which in the drawing is diagrammatically winding 9 of a transformer. Y

Owing to the large surface of the electrode the latter is not heated during the operation of the tube to a high temperature so that the magnesium layer only slightly volatilizes. Besides, the end 2 of the tube has such a shape that any distintegrating or volatilizing magnesium particles substantially strike on portions of the tube which are already coated with magnesium.

What we claim is 1. A discharge tube with positive column discharge and a leading-in conductor in the neighbourhood of which a portion of the wall of the tube is coated with a conductive layer which is at least partly covered by a magnerepresented by a secondary sium coating, this coating serving as an elecv trode.

2. A discharge tube with positive column discharge and a leading-in conductor in the neighbourhood of which a portion of the wall of the tube is coated with a graphite layer, which is at least partly covered by a magnesium coating, this coating serving as an electrode.

3. A discharge tube with positive column discharge and an electrode consisting of a wall covering of magnesium, the wall of the tube in the neighbourhood of the electrode being substantially spherical, so that the magnesium which has deposited on the wall and which volatilizes during theoperation of the tube substantially deposits again on the spherical part of the wall of the tube. V

. which at least partly is covered by a magnesium coating serving as an electrode, the wall of the tube in the neighbourhood of the electrode being substantially spherical so that the magnesium which has deposited on the wall and which volatilizes during the operation of the tube substantially deposits again on the spherical part of the wall of the tube.

5. A discharge tube with positive column discharge and a leading-in conductor in the,

neighbourhood of which a portion of the wall of the tube is coated with a graphite layer, which at least partly, is covered by a magnesium coating serving as an electrode, the Wall of the tube in theeneighbourhood of the electrode being substantially spherical so that the magnesium which has deposited on the wall and which volatilizes during the operation of the tube substantially deposits again on the spherical part of the wall of the tube.

6. In the manufacture of gas-filled discharge tubes for positive column discharge,

v the process of making an electrode which consists in coating the inner wall of the tube adjacent the leading-in conductor with a .con-

ductive layer and then heating a body consisting substantially of magnesium adjacent said layer to volatilize and deposit the magnesium thereon,

7. In the manufacture of gas-filled discharge tubes for positive column discharge,

the process of making an electrode which consists in coating the inner wall of the tube adjacent the leading-in conductor with a graphite emulsion and then heating a body consisting substantially of magnesium adjacent said graphite layer to volatilize and deposit the magnesium thereon in contact with the leading-in conductor. 7

8. A positive column discharge device comprising an envelope having a tubular portion with electrode chambers-of greater diameter than. said tubular portion at each end thereof, a lead-in member sealed into each electrode chamber and a metallic coating covering the inner wall of each electrode chamber, contacting with its respective lead-in member, and bounded by the junction of. the electrode chamber and tubular portion.

In testimony whereof we afiix our signas tures at the city of Eindhoven this 7th day of December, AD. 1925. I

GUSTAV ZECHER. I JOHANNES BRUIJNES" 

